Supply topology with power limiting feedback loop

ABSTRACT

A supply topology comprising an AC to DC or DC to DC adapter and an electronic device with an active system, a battery, and an adapter controller implements closed-loop control of adapter output voltage to limit power consumption by the electronic device to a value related to maximum adapter power. The adapter adjusts its output voltage in response to the magnitude of an error signal representing an amount by which instantaneous power consumption exceeds adapter maximum power. An adapter controller in the electronic device sets a limit for allocating current to battery charging from the signal representing maximum adapter power, with battery charging current approaching zero as instantaneous power consumption approaches maximum adapter power.

RELATED UNITED STATES PATENT APPLICATION

This application is a Continuation Application of the co-pending,commonly-owned U.S. patent application Ser. No. 11/520,943, filed Sep.13, 2006, by Doru Cioaca; Constantin Bucur; Alexandru Hartular andMarian Niculae, and entitled “Supply Topology With Power LimitingFeedback Loop”, the teachings of which are incorporated here byreference, which itself is a continuation-in-part of U.S. Nonprovisionalapplication Ser. No. 10/055,810, filed Jan. 23, 2002, now U.S. Pat. No.7,126,241, the teachings of which are incorporated here by reference,all of which claims the benefit of the filing date of U.S. ProvisionalApplication No. 60/309,459, filed on Aug. 1, 2001, the teachings ofwhich are also incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to power supply circuits, and moreparticularly, to power supply circuits having an adapter that generatesa signal related to available or maximum power and to electronic devicesconfigured to receive this signal. Particular utility for the presentinvention is in portable electronic devices; however, the presentinvention is equally applicable to any device that uses an adapter toprovide power.

BACKGROUND

Many electronic devices such as computers, cellular phones, radios,printers, and personal digital assistants use an alternating current(AC) to direct current (DC) adapter or DC to DC adapter to power thedevice and charge the device's batteries. For example, an AC to DCadapter (“AC/DC Adapter”. “AC Adapter”, or “Adapter”) plugs into an ACelectrical outlet and converts 100-240 volt, 50-60 Hz AC input voltageand current into a DC output voltage and current for use by anelectronic device. A DC to DC adapter converts a DC input current of onevoltage to a DC output current of another voltage. DC to DC adapters(“DC/DC Adapter”, “DC Adapter” or “Adapter”) are often used to powerelectronic devices from an accessory connector in a vehicle such as anautomobile, boat, or airplane.

Adapter output current and voltage are coupled to an input power rail inthe electronic device. For electronic devices having a battery or otherenergy storage device to supply operating power when an adapter isunavailable, output current and voltage from the battery or energystorage device are also coupled to the input power rail. Othercomponents connected to the input power rail detect the presence of anadapter or battery, convert adapter output voltage and battery outputvoltage to other voltages used by active systems within the electronicdevice, and charge the battery.

For conventional power supply circuits, a value for maximum adapterpower is generally chosen to be large enough to simultaneously supplythe loads from active systems in the electronic device and batterycharging. Also, adapters used in conventional power supply circuitsgenerally have an output voltage that is substantially higher than thebattery output voltage. For example, in an electronic device with athree-cell lithium-ion battery, the battery output voltage on the inputpower rail varies between about 9 volts DC (VDC) and about 13.5 VDC,depending on battery charge condition. With a conventional supply powersupply circuit, adapter output voltage on the input power rail varies ina range from about 16.8 VDC to about 19 VDC and components connected tothe input power rail are rated to withstand about 30 VDC to allow fordesign margins. The large difference between the output voltage ofconventional adapters and battery output voltage affects the cost andsize of components connected to the input power rail. Components ratedto withstand 30 V are larger and more expensive than components ratedfor lower voltages. Furthermore, voltage converters and other componentsoperate at lower electrical efficiency from adapter input power comparedto battery power when the difference between adapter voltage and batteryvoltage is large. Lower electrical efficiency causes increaseddissipation within the electronic device and affects many systemparameters such as component operating temperatures, size and cost ofactive and passive cooling components, printed circuit board area, andenclosure size and complexity.

Recent efforts have sought to improve conventional power supply circuitsby including a power allocation controller in the electronic device toapportion adapter output power between active systems and batterycharging. In an exemplary power supply circuit, a power allocationcontroller reduces battery charging current when power consumed by theelectronic device exceeds a fixed allocation limit corresponding tomaximum adapter current. In another exemplary power supply circuit, thefixed allocation limit corresponds to maximum adapter power. Anallocation controller permits the use of a smaller adapter compared toconventional power supply circuits because the maximum load from activesystems and the maximum load from battery charging do not occurconcurrently.

A power allocation controller is generally configured for a particularfixed allocation limit by connecting resistors or other components toprogramming inputs on the power allocation controller. However, ifalternate adapters requiring different allocation limits are availableto be coupled to an electronic device, for example a lightweight traveladapter with a small maximum power rating and a larger docking stationadapter or fast-charge adapter with a higher maximum power rating, thepower allocation controller in the electronic device will be unable toadjust its operation to the allocation limit associated with eachalternate adapter, using instead the fixed allocation limit set at thetime the electronic device was manufactured. Mismatched allocationlimits raise the possibility that battery charging will not proceed at adesired rate or that the maximum adapter power may be exceeded by theelectronic device. An example of power allocation control with a fixedpower allocation limit is provided in U.S. Pat. No. 6,611,129.

Other efforts have been directed at passing one or more fixed valuesrelating to adapter specifications such as maximum current or maximumpower from an adapter to an electronic device modified to receive thevalues. An electronic device modified to receive fixed values related toadapter parameters can determine how much adapter output current toallocate between battery charging circuits and active systems or makeother decisions about operating modes for the electronic device. In oneexemplary power supply circuit, an electronic device receivesinformation about an adapter but does not use the information to modifythe adapter's output voltage, that is, there is no closed-loop controlof adapter output voltage by the electronic device. Without closed-loopcontrol of adapter output voltage, the necessity for a large differencebetween adapter output voltage and battery voltage remains, leading tolower power efficiency as earlier described. An example is provided inU.S. Pat. No. 6,058,034.

SUMMARY

In one aspect the present invention provides a supply circuit with an ACto DC or DC to DC adapter coupled to an electronic device comprising anadapter controller, a rechargeable battery, and an active system forimplementing one or more functions provided by the electronic device.The adapter generates DC output current and voltage for supplying powerto the adapter controller and active system and for charging thebattery. In one embodiment, the difference between the adapter outputvoltage and the battery voltage is a few hundred millivolts, a smallfraction of the difference between adapter voltage and battery voltagein a conventional adapter. The adapter portion of one embodiment of theinvention generates a reference voltage related to the maximum adapterpower. The reference voltage is coupled to an adapter control lineconnected from the adapter to the electronic device and to the adaptercontroller. The adapter controller generates a signal related toinstantaneous power consumption by the electronic device from an inputsignal related to adapter output voltage and a signal related to currentconsumption and compares the instantaneous power consumption signal tothe reference voltage representing maximum adapter power. The adaptercontroller uses the result of the comparison to form an adapter controlsignal whose magnitude is zero when instantaneous power consumption isless than or equal to maximum adapter power, otherwise the adaptercontrol signal has a magnitude related to the difference betweeninstantaneous power consumption and maximum adapter power. The adaptercontroller couples the adapter control signal to the adapter controlline.

The adapter receives the adapter control signal and adjusts the adapteroutput voltage in response to the magnitude of the adapter controlsignal. For an adapter control signal of zero magnitude, correspondingto a condition where instantaneous power consumption is less than orequal to maximum adapter power, the adapter output voltage is held toits nominal value, plus or minus regulation tolerances. An adaptercontrol signal of nonzero magnitude causes a related decrease in adapteroutput voltage, corresponding to a decrease in the power consumption ofthe electronic device. The adjustment of adapter output voltage by acontrol signal formed by the adapter controller from a comparisonbetween instantaneous power consumption and a limit corresponding tomaximum adapter power represents closed-loop control by the adaptercontroller.

In another aspect, the reference voltage related to maximum adapterpower, coupled to the adapter controller on the adapter control line,represents a control limit below which the adapter controller permitsadapter output power to be shared between the active system and abattery in the electronic device. Power for charging the batteryapproaches zero as power consumed by the active system approaches themaximum adapter power. When the sum of the power consumed by the activesystem and by battery charging exceeds the control limit, adapter outputvoltage, and consequently power for charging the battery, is reduceduntil the adapter output power control loop stabilizes withinstantaneous power consumption equal to maximum adapter power. Furtherincreases in power consumption by the active system cause furtherreductions in power for battery charging, until the active system isconsuming the maximum adapter power and no battery charging occurs. Inone embodiment, if the active system increases power consumption beyondthe maximum adapter power, the battery supplies power to the activesystem. Conversely, as power drawn by the active system falls belowmaximum adapter power, an increasing amount of power is available fromthe adapter for battery charging. When the active system is in aquiescent state, most of the adapter's maximum power is available forbattery charging.

This section summarizes some features of the invention. These and otherfeatures, aspects, and advantages of the embodiments of the inventionwill become better understood with regard to the following descriptionand upon reference to the following drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram for one embodiment of the invention.

FIG. 2 shows a schematic of one embodiment of an adapter.

FIG. 3 shows a schematic of one embodiment of an electronic devicecomprising an active system, a battery, and an adapter controller.

DESCRIPTION

The embodiments described in this section illustrate but do not limitthe invention. The invention is not limited to any particular circuitry,voltage values, current values, battery chemistry, or other parameters.

FIG. 1 depicts a block diagram of one embodiment of the invention. As abroad overview, an AC to DC adapter 100 converts an AC input voltage toa DC output voltage through the operation of a power converter. In oneembodiment, the power converter is a flyback converter. The adapter's DCoutput voltage and current are coupled to input terminals on anelectronic device 200 comprising an input power rail represented by line206, an active system 202, a rechargeable battery 204, and an adaptercontroller 300. In one embodiment, the rechargeable battery 204 is alithium ion battery. In other embodiments, lithium ion polymer, nickelmetal hydride, nickel cadmium, lead-acid, or other rechargeablebatteries or equivalent rechargeable storage devices for electricalenergy are used. The active system 202 comprises the electrical andelectronic components that implement the functionality provided by theelectronic device 200. The adapter controller 300 measures voltages andcurrents related to the adapter 100, active system 202, and battery 204,and implements closed-loop control of adapter output to efficientlycharge the battery 204 and supply the power demands of the active system202.

The adapter controller 300 measures input voltage to the electronicdevice 200 and another voltage related to current consumption by theelectronic device 200 and generates a signal representing instantaneouspower consumption. The adapter controller 300 compares the signalrepresenting instantaneous power consumption to a reference signal fromthe adapter 100 that is related to the value of maximum adapter powerand generates a control signal current output that is related to anamount by which instantaneous power consumption exceeds the maximumadapter power. The control signal current output is coupled to anadapter control line connected between a terminal CTR on the electronicdevice 200 and the corresponding CTR terminal on the adapter 100 andrepresents a feedback signal from the adapter controller 300 to theadapter 100. The output of the power converter in the adapter 100 ismodified in response to the magnitude of the control signal, enablingclosed-loop control of adapter 100 output. The control loop operates tocause a decrease in adapter output voltage related to the magnitude ofthe control signal current from the adapter controller 300.

Placing the output voltage of the adapter 100 under closed-loop controlcauses the adapter's output voltage to remain within a small range closeto the battery output voltage. In many types of electronic devices, thecurrent drawn by the active system 202 is adjusted by the active system202 in response to changes in adapter output voltage, in effectmaintaining constant power consumption by the active system 202. Currentavailable for battery charging is therefore the difference betweenoutput current from the adapter 100 and current drawn by the activesystem 202, minus a small amount of current consumed by the adaptercontroller 300. When power consumed by the active system 202 alone issufficient to cause instantaneous power consumption to exceed themaximum adapter power, the adapter output voltage is reduced by theaction of closed-loop control until the adapter output voltage isessentially equal to the battery voltage, reducing current flow into thebattery 204 and eventually ending battery charging. Conversely, when theactive system 202 is in a quiescent or low-power state, an increasingamount of power, up to the maximum power output of the adapter 100, isavailable for charging the battery 204.

FIG. 2 shows the adapter portion of one embodiment. An adapter 100comprises a flyback converter 106, an operational amplifier U1 108, arectifier CR1 102, and resistors R_(A) 104 and R_(B) 110. The inputvoltage and current to be converted to DC output by the adapter 100 arecoupled to the flyback converter 106 on terminals V_(IN+) and V_(IN−).In one embodiment the input voltages coupled to terminals V_(IN+) andV_(IN−) are AC voltages. In another embodiment the input voltages are DCvoltages. The design of flyback converters is well known in the art andwill not be described herein. One skilled in the art will recognize thatother power converter configurations may be used instead of a flybackconverter to convert input voltages and currents to DC output. The DCoutput of the flyback converter 106 is connected to the anode of arectifier CR1 102. The cathode of the rectifier CR1 102 is connected toan output terminal V_(OUT). A resistor R_(A) is connected between theterminal V_(OUT) and a terminal CTR, and a resistor R_(B) is connectedbetween the terminal CTR and a terminal GND. The terminal GND is theground reference connection for the adapter. Resistors R_(A) and R_(B)determine the nominal output voltage V_(AD) of the adapter 100. In theembodiment shown in FIG. 2, the terminal CTR couples voltage V_(REF)from the adapter to an adapter controller in an electronic device, andfurther couples an adapter control current signal from the adaptercontroller to the adapter. In an alternate embodiment, a fourth terminalis added for connections between the adapter and an electronic device,and voltage V_(REF) and the adapter control current signal are coupledto different terminals.

The output of an operational amplifier U1 108 is connected to a dutycycle control input to the flyback converter 106. Increasing the voltageon the duty cycle control input causes the adapter output voltage V_(AD)to increase. Decreasing the duty cycle input control voltage causesV_(AD) to decrease. The inverting input of operational amplifier U1 108is connected to the adapter 100 terminal CTR. The inverting input ofoperational amplifier U1 108 is further connected to the voltage dividerformed by the resistors R_(A) 104 and R_(B) 110. The noninverting inputof operational amplifier U1 108 is connected to a reference voltageV_(REF) on line 112. A value for V_(REF) is chosen when the adapter 100is designed such that V_(REF) is related to the maximum power outputP_(ADMAX) from the adapter 100. One skilled in the art will recognizethat an alternative to selecting a value for V_(REF) 112 correspondingto P_(ADMAX) is to select a fixed value of V_(REF) and replace resistorR_(A) 104 with two or more resistors in series, the resistors in serieshaving a combined resistance equal to R_(A) 104. The values of theindividual series resistors are selected so that the voltage drop acrosseach resistor, plus V_(REF), cumulatively sum to the desired referencevoltage corresponding to the maximum power output P_(ADMAX) from theadapter 100, and the adapter 100 terminal CTR is connected to thecorresponding resistor.

Terminals V_(OUT), CTR, and GND on adapter 100 are connected to thecorresponding terminals V_(IN), CTR, and GND on electronic device 200,as shown in FIG. 1. An adapter control current flows from the adaptercontroller 300 into the adapter 100 terminal CTR. Inside adapter 100,the adapter control current flows through resistor R_(B) 110 to ground,generating a voltage at the inverting terminal of the operationalamplifier U1 108 that increases as the adapter control currentincreases. The output of operational amplifier U1 108 is related to thedifference between V_(REF) 112 and the voltage across resistor R_(B)110, the output decreasing as the voltage across resistor R_(B) 110increases. When the adapter control current has a value of zero (nocurrent flow), the adapter output voltage V_(AD) remains at its nominalvalue within the regulation limits of the adapter 100. As the adaptercontrol current increases the output of U1 108 decreases, causing acorresponding decrease in V_(AD).

FIG. 3 depicts one embodiment of an electronic device 200 having anadapter controller 300, an active system 202 for implementing thefunctions provided by electronic device 200, and a rechargeable battery204. In other embodiments, the battery 204 is replaced with anotherrechargeable energy storage device, such as a rechargeable capacitivestorage device. Output current I_(AD) from the adapter 100 flows intoinput terminal V_(IN) on the electronic device 200, through one or moresense resistors represented by R_(SENSE) 208, and into the active system202, a battery 204, and the adapter controller 300. Adapter outputvoltage V_(AD) is coupled through terminal V_(IN) to R_(sENSE) 208.Inside the adapter controller 300, a current sense amplifier CSA 304measures the differential voltage across sense resistor R_(SENSE) 208and outputs a signal related to current drawn by the electronic device200. The signal related to current is one input to the Power Sense 306functional block. A second input to the Power Sense 306 functional blockis from a line coupled to terminal V_(IN), corresponding to the value ofthe DC input voltage to the electronic device 200. The output of thePower Sense 306 functional block is a signal related to instantaneouspower consumption by the electronic device 200. One skilled in the artwill be familiar with the design of circuits to generate an outputsignal related to power from input signals related to voltage andcurrent.

The output of the Power Sense 306 functional block is connected to afirst input of an error amplifier ERR 308. A second input of erroramplifier ERR 308 is coupled to terminal CTR and to the output of avoltage-controlled current source (VCCS) 302 on line 310. The design ofvoltage-controlled current sources is well known in the art and will notbe described herein. The output of error amplifier ERR 308 connects tothe control input of the VCCS 302 on line 312. A voltage supply inputfor the VCCS 302 is coupled to line 206, the input power rail for theelectronic device 200.

The system input power rail 206 connects from sense resistor R_(SENSE)208 to a first terminal of the battery 204 and to a power input terminalon the active system 202. The voltage on the system input power rail 206is equal to adapter output voltage V_(AD) minus a small voltage acrosssense resistor R_(SENSE) 208 when an adapter 100 is present and tobattery voltage V_(BAT) when an adapter 100 is not present. V_(AD) isgenerally a few hundred millivolts higher than V_(BAT).

During operation, the voltage at the adapter terminal CTR is held to thevalue V_(REF) by operational amplifier U1 108. The voltage on line 310,applied to the second input of error amplifier ERR 308, is also equal tovoltage V_(REF) and is therefore related to the maximum adapter powerP_(ADMAX). The voltage at the first input to error amplifier ERR 308represents instantaneous power consumption by the electronic device, aspreviously described. The output of error amplifier ERR 308 on line 312is a voltage signal whose magnitude is related to the amount by whichinstantaneous power consumption exceeds P_(ADMAX). The VCCS 302 acceptsthe voltage signal on line 312 and generates on line 310 an outputcurrent whose magnitude is related to the amount by which instantaneouspower consumption exceeds P_(ADMAX). The current output from the VCCS302 on line 310 is zero while instantaneous power consumption is lessthan or equal to P_(ADMAX). Current flowing from the VCCS 302 throughterminals CTR into the adapter 100 causes a related decrease in theoutput voltage of the adapter 100 as previously described.

Line 310 performs two functions in the current embodiment. Line 310couples a voltage signal from the adapter 100 to the error amplifier ERR308 in the adapter controller 300. The voltage signal corresponds to themaximum adapter power P_(ADMAX) and serves as a control threshold forclosed loop control of adapter output voltage by the electronic device.Line 310 also couples a current signal from the VCCS 302 in the adaptercontroller 300 to the inverting input of U1 108 in the adapter 100. Thecurrent signal represents the amount by which instantaneous powerconsumption exceeds P_(ADMAX) and functions as a feedback signal formodifying adapter output. Signals flowing bidirectionally on line 310enable the electronic device 200 to achieve closed-loop control ofadapter output voltage, detect maximum power differences betweenalternate adapters, manage power allocation, and control powerconsumption to prevent maximum adapter power from being exceeded. In analternate embodiment, the voltage signal corresponding to P_(ADMAX) fromthe adapter is coupled to the electronic device and then to the erroramplifier ERR 308 on a terminal separate from terminal CTR and thecurrent signal from the VCCS 302 is coupled on line 310 to terminal CTR.

While instantaneous power consumption remains less than P_(ADMAX),adapter 100 output current I_(AD) flows to both the active system 202and the battery 204. The amount of current available for batterycharging is the difference between I_(AD) and the current drawn by theactive system, minus a small amount consumed by the adapter controller300. When instantaneous power consumption exceeds P_(ADMAX), the adapter100 output voltage V_(AD) decreases under closed-loop control by erroramplifier ERR 308 until instantaneous power consumption reaches controlequilibrium with P_(ADMAX). Decreasing V_(AD) causes a correspondingdecrease in charging current to the battery 204. As power consumption bythe active system increases toward the maximum adapter power, V_(AD)decreases toward the battery voltage and battery charging reduces tozero. Further increases in power consumption by the active system causeV_(AD) to decrease to slightly less than the battery voltage and, in oneembodiment, current flows out of the battery 204 and into the activesystem 202. Diodes and a switch (not shown) in line 206 prevent currentfrom flowing from the battery 204 into the adapter 100. The adapter 100reference voltage V_(REF) on line 112 in FIG. 2 can therefore beunderstood to represent the limit above which the adapter controller 300allocates adapter output power away from the battery 204 and toward theactive system 202. If a battery 204 is not present or is discharged andinstantaneous power consumption remains greater than P_(ADMAX) due topower drawn by the active system 202, protection circuits within flybackconverter 106 act to prevent overload damage to adapter 100. The designof overload protection circuits for adapters is well known in the artand will not be described herein.

In some embodiments, the output of more than one error amplifier iscoupled to line 312, the control input of the VCCS 302. Each erroramplifier with output connected to line 312 separately compares ameasured value against a reference value for a parameter of interest.When the signal representing the measured value of the parameter ofinterest exceeds a control limit representing the reference value of theparameter of interest, the corresponding error amplifier generates avoltage signal on line 312, causing the VCCS to output a current signalon line 310 that leads to a corresponding decrease in adapter 100 outputvoltage, thereby implementing closed-loop control of the adapter outputbased on the parameter of interest. Multiple control loops may operatesimultaneously, but the action of any one error amplifier in a systemcomprising multiple control loops is sufficient to cause a controlcurrent to be generated on line 310 to achieve closed loop control ofadapter 100. In one embodiment, a control loop for adapter outputcurrent I_(AD) is added to the adapter controller 300 by adding an erroramplifier and providing a measured value and a limiting reference valuefor adapter output current as inputs to the error amplifier. In anotherembodiment, a control loop for battery voltage is added to the adaptercontroller 300. In another embodiment, a control loop for battery chargecurrent is added to adapter controller 300.

In one embodiment, amplifiers CSA 304 and ERR 308 are implemented asoperational transconductance amplifiers. In another embodiment,amplifiers CSA 304 and ERR 308 are implemented as operationalamplifiers. One skilled in the art will recognize that the functionsperformed by amplifiers CSA 304 and ERR 308 may be achieved withoperational amplifiers or transconductance amplifiers.

The present disclosure is to be taken as illustrative rather than aslimiting the scope, nature, or spirit of the subject matter claimedbelow. Numerous modifications and variations will become apparent tothose skilled in the art after studying the disclosure, including use ofequivalent functional and/or structural substitutes for elementsdescribed herein, use of equivalent functional couplings for couplingsdescribed herein, or use of equivalent functional steps for stepsdescribed herein. Such insubstantial variations are to be consideredwithin the scope of what is contemplated here. Moreover, if pluralexamples are given for specific means, or steps, and extrapolationbetween or beyond such given examples is obvious in view of the presentdisclosure, then the disclosure is to be deemed as effectivelydisclosing and thus covering at least such extrapolations.

RESERVATION OF EXTRA-PATENT RIGHTS, RESOLUTION OF CONFLICTS, ANDINTERPRETATION OF TERMS

After this disclosure is lawfully published, the owner of the presentpatent application has no objection to the reproduction by others oftextual and graphic materials contained herein provided suchreproduction is for the limited purpose of understanding the presentdisclosure of invention and of thereby promoting the useful arts andsciences. The owner does not however disclaim any other rights that maybe lawfully associated with the disclosed materials, including but notlimited to, copyrights in any computer program listings or art works orother works provided herein, and to trademark or trade dress rights thatmay be associated with coined terms or art works provided herein and toother otherwise-protectable subject matter included herein or otherwisederivable herefrom.

If any disclosures are incorporated herein by reference and suchincorporated disclosures conflict in part or whole with the presentdisclosure, then to the extent of conflict, and/or broader disclosure,and/or broader definition of terms, the present disclosure controls. Ifsuch incorporated disclosures conflict in part or whole with oneanother, then to the extent of conflict, the later-dated disclosurecontrols.

Unless expressly stated otherwise herein, ordinary terms have theircorresponding ordinary meanings within the respective contexts of theirpresentations, and ordinary terms of art have their correspondingregular meanings.

1. An adapter controller, comprising: a comparison circuit operable forcomparing a first signal representative of an instantaneous powerconsumption of an electronic device to a reference signal representativeof maximum adapter power of an adapter configured to power saidelectronic device, and for generating an error signal representative ofan amount by which said first signal exceeds said reference signal; anda control circuit coupled to said comparison circuit and operable foradjusting an output of said adapter according to said error signal. 2.The adapter controller of claim 1, wherein said control circuitcomprises a voltage controlled current source operable for receivingsaid error signal and for generating a current representative of saidamount by which said instantaneous power consumption exceeds saidmaximum adapter power.
 3. The adapter controller of claim 1, wherein acontrol signal from said control circuit is transferred from saidadapter controller to said adapter via a control line coupled betweensaid adapter and said adapter controller, and wherein said referencesignal is transferred from said adapter to said adapter controller viasaid control line.
 4. The adapter controller of claim 1, wherein saidelectronic device comprises an active system for performing at least onefunction and a battery charged by said adapter.
 5. The adaptercontroller of claim 4, wherein power for charging said battery isreduced if said instantaneous power consumption exceeds said maximumadapter power.
 6. The adapter controller of claim 4, wherein an outputcurrent of said adapter flows to both said active system and saidbattery if said instantaneous power consumption is less than saidmaximum adapter power.
 7. The adapter controller of claim 4, whereinpower for charging said battery is reduced when power consumed by saidactive system approaches said maximum adapter power.
 8. The adaptercontroller of claim 1, wherein said output of said adapter remains at anominal level when said first signal is not greater than said referencesignal.
 9. The adapter controller of claim 1, wherein said output ofsaid adapter is reduced based on said error signal until saidinstantaneous power consumption is reduced to said maximum adapterpower.
 10. A method, comprising: powering an electronic device by anadapter; receiving a reference signal representative of maximum adapterpower of said adapter; receiving a second signal representative ofinstantaneous power consumption of said electronic device; generating acontrol signal representative of an amount by which said second signalexceeds said reference signal; and adjusting an output voltage of saidadapter according to said control signal.
 11. The method of claim 10,further comprising: reducing said output voltage of said adapteraccording to said control signal until said second signal is reduced tosaid reference signal.
 12. The method of claim 10, wherein saidelectronic device comprises an active system for performing at least onefunction and a battery.
 13. The method of claim 12, further comprising:reducing power to said battery if said second signal exceeds saidreference signal.
 14. The method of claim 12, further comprising:terminating charging said battery if power consumed by said activesystem is increased to said maximum adapter power.
 15. The method ofclaim 12, further comprising: supplying power from said battery to saidactive system if power consumed by said active system exceeds saidmaximum adapter power of said adapter.
 16. The method of claim 10,wherein said output voltage of said adapter remains at a nominal levelwhen said second signal is not greater than said reference signal.
 17. Apower supply system, comprising: an adapter operable for generatingoutput power and a first reference signal representative of a parameterof said adapter, and for adjusting said output power according to acontrol signal; and an adapter controller coupled to said adapter andoperable for comparing said first reference signal with a second signalrepresentative of an operating parameter of an electronic device, andfor generating said control signal representative of an amount by whichsaid second signal exceeds said first reference signal.
 18. The powersupply system of claim 17, wherein said parameter of said adaptercomprises maximum adapter power of said adapter.
 19. The power supplysystem of claim 17, wherein said operating parameter of said electronicdevice comprises instantaneous power consumption of said electronicdevice.
 20. The power supply system of claim 17, further comprising: acontrol line coupled between said adapter and said adapter controller,wherein said control signal is transferred from said adapter controllerto said adapter via said control line and wherein said first referencesignal is transferred from said adapter to said adapter controller viasaid control line.
 21. The power supply system of claim 17, wherein saidadapter comprises an amplifier operable for comparing said controlsignal to a second reference signal and for generating an output signal,and wherein said adapter is configured to adjust said output poweraccording to said output signal.
 22. The power supply system of claim21, wherein said electronic device comprises a battery and an activesystem, and wherein said second reference signal represents a limitabove which said adapter controller allocates said output power awayfrom said battery and toward said active system.
 23. The power supplysystem of claim 17, wherein said output power of said adapter is reducedaccording to said control signal until said second signal is reduced tosaid first reference signal.